Gas turbine powerplants

ABSTRACT

A gas turbine powerplant for operation with heat from nuclear or fossil fuel comprises a circulatory system which contains the gaseous working medium for a turbine and has a recuperative heat exchanger in series with the turbine and the heat supply. The system has a plurality of compressors of which two form respective paths for parallel flows of medium and are connected to respectively different temperature stages of the recuperative heat exchanger at the high-pressure side thereof. The compressors are connected through cooling means with the heat supply within the circulatory system. The median specific heat of the gaseous medium at the high-pressure side of the recuperative heat exchanger is more than 5 percent higher than at the low-pressure side, and the suction pressure of at least one of the two compressors at full load is above the critical pressure.

United States Patent [72] Inventor Hans-Peter Schabert Friedrich Bauer Str. 30, Erlangen, Germany [2]] Appl. No. 816,520 [22] Filed Apr. 16, 1969 [45] Patented June 8, 1971 [32] Priority Apr. 24, 1968 [33] Germany [3i] P 17 51 226.4

[54] GAS TURBINE POWERPLANTS 12 Claims, 7 Drawing Figs.

52 1 U.S. Cl 60/36, 60/59 [51] Int. Cl ..F0lk 25/00, FOlk 3/18 [50] Field of Search 60/36, 59 T [56] References Cited UNITED STATES PATENTS 2,203,731 6/l940 Keller 60/59 T 3,324,652 6/1967 Maillet 3,444,038 5/]969 Hans-PeterSchabert....

ABSTRACT: A gas turbine powerplant for operation with heat from nuclear or fossil fuel comprises a circulatory system which contains the gaseous working medium for a turbine and has a recuperative heat exchanger in series with the turbine and the heat supply. The system has a plurality of compressors of which two form respective paths for parallel flows of medium and are connected to respectively different temperature stages of the recuperative heat exchanger at the high-pressure side thereof. The compressors are connected through cooling means with the heat supply within the circulatory system. The median specific heat of the gaseous medium at the high-pressure side of the recuperative heat exchanger is more than 5 percent higher than at the low-pressure side, and the suction pressure of at least one of the two compressors at full load is above the critical pressure.

- a a 5 E o a. s R "30 /0 2 g 57ata g 15 .2: g2? 191; as. 3 #20" ,2" 1- l en a 2 t I 37 32 3a 36 22 2 I a mamas L Qlata 79 PATENTED JUN 8 ISYI sum 2 or 3 1 sun" 30Uata 350 m GAS TURBINE POWERPLANTS My invention relates to gas turbine powerplants operating with heat from nuclear or fossil fuel, and in one of its aspects to gas turbine powerplants operating with carbon dioxide (CO as the working medium.

The essential components of such a powerplant are a heat source, a gas turbine, recuperative heat exchanger, compressor and cooler.

There are known proposals to convert thermal energy obtained, for example, from fossil fuels to electrical energy with the aid of gas turbine processes. Aside from other gases whose critical pressure and temperature data are favorable for such purposes, the relatively inert gas CO has been repeatedly mentioned in such proposals as the working medium for operating the gas turbines. Reference in this respect may be had, for example, to the periodical Journal of Engineering For Power," Apr. 1967, pages 229 to 236 and to my copending applications Ser. No. 651,876, filed July 7, I967; Ser. No. 767,l26, filed Oct. 14, 1968 and Ser. No. 772,640, filed Nov. 1, 1968. In the gas turbine process described in the journal there occurs a condensation of the working medium so that the compressor inducts a mixture of liquid and gas. This entails the danger of cavitation phenomena. The patent applications mentioned above refer to gas turbine circulatory systems with recuperative heat exchangers at which large differences in specific heat of the working medium occur between the high-pressure side and the low-pressure side. Such differences impair the overall efficiency of the powerplant. This obviates an appreciable amount of the gain theoretically obtainable by the high density of the working medium obtainable with the rated power consumption of the compressor.

It is an object of my invention to improve the efficiency of gas turbine plants while simultaneously securing a compact design and avoiding the complication introduced by such intermediate superheating as has also been proposed previously.

Another object of the invention, subsidiary to the one just mentioned, is to devise a powerplant that it particularly well suitable for operation with nuclear reactors cooled by sodium gas and which is also suitable for gas turbines connected to other types of heat sources.

According to the invention the median specific heat of the gaseous working medium at the high-pressure side of the recuperative heat exchanger is more than percent higher than on the low-pressure side, at least two compressors being provided of which two, serving as partial flow compressors, are connected to different temperature stages respectively at the high-pressure side of the recuperative heat exchanger; and high-pressure gas coming form the compressors is supplied to the recuperative heat exchanger in the from of two partial flows. For this purpose the heat exchanger may be provided, for example, with a tap in its system of tube windings. However, separate windings of heat exchanger tubes for the respective two component flows of compressed working medium are also applicable.

Due to such a subdivided supply of the compressed highpressure gas, the great difference in specific heat of the working turbine circulatory the high and low-pressure sides is compensated thus increasing the efficiency. In spite of the additional power required for the compressors inserted into the coolant's partial flows, the heating requirements of the entire plant are so greatly reduced that even with turbine intake temperatures of only 500 C., a turbine process of more than 40 percent thermal efficiency is obtainable. The supercritical state of induction of the gaspreferably CO ahead of the compressor has the advantage that a power regulation through regulation of the throughput of medium by weight, can be secured in a simple manner by changing the temperature setting at the outlet of the cooler. As will be recognized from FIG. 2a, there is no danger that liquified gas may occur in the system since the process remains within the supercritical range of the gas.

For further explaining the invention, the accompanying drawing illustrates a variety of embodiments by way of example:

FIGS. 1 and 2 are schematic circuit diagrams of two powerplants operating with heat from a sodium-cooled nuclear reactor;

FIGS. 2a and 2b are explanatory temperature-pressure diagrams for explaining the operation of the gas turbine circulatory system of such plants;

FIG. 3 is a schematic circuit diagram of a plant directly heated from a nuclear reactor;

FIG. 4 is another temperature-pressure diagram of the cycle operation in a system somewhat modified from that of FIG. 4; and

FIG. 5 is the schematic circuit diagram ofa gas turbine plant heated with fossil fuel and operating according to the performance diagram of FIG. 4.

Corresponding components of the system are denoted by the same respective reference numerals in the various illustratrons.

FIG. 1 illustrates an example of a circulatory system for a sodium-heated CO gas turbine plant with partialflow compression and precompression. The original heat generator is a sodium-cooled nuclear reactor plant which is not illustrated. The heat generated by the reactor is applied to a heat exchanger 10 which transfers the heat to the gas circulation system thus forming part of the heat source means of that system. Mutually corresponding temperature and pressure relations are indicated at the respective circuit localities of the system. The gas current, heated in the source exchanger 10 and having a temperature of 500 C. at a pressure of 300 ata. (atmospheres above ambient) passes through two valves 30 and 31 in two partial flows to respective turbines 18 and 14. The turbine 14 is the main prime mover and serves for driving a precompressor 16, a main compressor 18 and an electric current generator 15. The auxiliary turbine 13 drives an auxiliary compressor 17. After the pressure of the working gas is reduced to 57 ata. in the turbines l3 and 14, the gas arrives at a temperature of 320 C. at a recuperative heat exchanger 19 where it transfers its residual heat to the coolant which recycles back to the source heat exchanger 10. From the recuperative exchanger 19 (recuperator) the working gas reaches a cooler 22 at a temperature of C. Upon being cooled to 35 C., the working medium arrives at the precompressor l6 driven from the main turbine 14. Approximately 30 percent of the working medium are branched off behind the main turbine 14 and pass as a first partial flow to the auxiliary compressor 17. The other partial flow, amounting to 70 percent passes through another cooler 21 to the main compressor 18. The working medium leaving the compressor 18 flows through a check valve (flap valve) 33 and thence through the tube windings of the recuperator 19 at an entering temperature of about 68 C. The partial flow coming form the auxiliary compressor 17, not having passed through the second cooler 21, has a higher temperature, namely C., an is supplied through a check (flap) valve 32 to a tap point a of the highpressure tube windings 20. Thus in the upper half of the stack of tubes the two partial currents are again combined to a single flow of working medium which returns to the source heat exchanger 10 at a temperature of 273 C., and a pressure of 305 ata.

For the normal operation at rated full load described in the foregoing, the check valves 37 and 36 are closed, and the valves 30, 31, 32 and 33 are open. In the event a rapid stoppage of the turbine is required, a bypass valve 36 is opened. When the system is to operate at partial load (such as a fraction of the rated full load), the auxiliary turbine 13 can be shut down by closing the valve 30. For restarting the auxiliary turbine 13, the valves 30 and 37 are open in a regulated manner; the valve 37 then acts as a bypass valve and the auxiliary cooler 23 prevents an excessive temperature increase during startup performance.

FIG. 2 shows a somewhat simplified circuit ofa similar sodium-heated CO turbine plant in which the above-mentioned precompressor l6 and the cooler 22 are omitted. The division into partial flows or currents of working gas is effected before the gas enters into the cooler 2]. Thirty percent of the medium pass through the valve 35 and the compressor 17 through the check valve 32 at a temperature of 197 C. to enter at point a of the stack 20 of tube windings in the recuperator 19. The major portion of the working medium traverses the cooler 21 and arrives at the compressor 18 at a temperature of 33 C. and a pressure of 90 ata. From compressor 18 the gas enters into the lower end of the winding stack 20 at 310 ata. and 68 C. The partial currents of working medium, combined in the stack 20, pass as a single current through the recuperative heat exchanger 19 at 305 ata. and 237 C. before returning to the source heat exchanger 10. The normal operation just described with reference to FIG. 2 requires that the valves 35, 32 and 30 be open, the valve 30 being regulated if desired. The valves 34, 36 and 38 are closed during such operation.

For partial load operation of the system, the compressor 17 and the turbine 13 can be shut down by closing the valve 30. If nothing else is done, the outlet temperature at the recuperator 19 increases at the high-pressure side. For preventing an excessive or undesired temperature increase of this kind, the valves 35 and 32 are to be additionally closed. For restarting the partial flow compressor 17, the valves 38, 35, 34 and 30 are opened in a regulated manner, and the cooler 21 then additionally assumes the function of the auxiliary cooler 23 in FIG. 1. After startup, the valve conditions are the same as for normal operation. As in the system of FIG. 1, rapid shutdown is effected by completely opening the bypass valve 36.

In contrast to the embodiments so far described, FIG. 3 illustrates a circuit in which a nuclear reactor 1] is used as a direct heat source in the gas turbine circulatory system. That is, the working medium of the gas turbine simultaneously constitutes a coolant for the nuclear reactor, a separate primary circuit in the reactor, for example a circulation of sodium in the reactor, being dispensed with. In accordance with the above-mentioned application Ser. No. 651,876, the coolant heated in the nuclear reactor does not directly reach the turbine but first passes through the recuperative heat exchanger 19. The pressure reduction of the working medium in the main turbine 14 occurs before the coolant reenters into the reactor 11. This, among other things, affords preventing the nuclear reactor from being impressed by the maximum pressure of the turbine system.

In other respects the system of FIG. 3 is similar to those of FIGS. 1 and 2. That is, the current or working medium, after leaving the recuperative heat exchanger 19, is subdivided. A partial flow of 25 percent passes through the auxiliary compressor l7, and another flow of 75 percent passes through the cooler 21 to the main compressor 16. Both partial currents are recombined in the stack of tube windings 20 in the recuperator 19, substantially as described with reference to FIGS. 1 and 2. After leaving the recuperator 19, the working medium reaches the turbines l3 and 14 at 300 ata. and 436 C. Upon leaving the turbines, the working medium, now having a pressure of 120 ata. and a temperature of 334 C., returns to the nuclear reactor 11 to serve as a coolant therein.

For normal operation of the system shown in FIG. 3, the valves 30, 35 and 32 are open, and the partial valves 36 and 34 are closed. For partial load operation, the auxiliary compressor 17 is to be shut down. For restarting, the valve 35 is partially closed to provide for mixed cooling, and the valve 36 is opened. The bypass valve 34 and the valve 30 are opened approximately in synchronism with each other. Upon reaching the rated speed of the auxiliary turbine 13, the valve 34 is closed and the initial valve condition for normal operation is reestablished, so that the partial flow delivered through the auxiliary compressor 17 can enter into the recuperator exchanger 19.

Another circuit system for simultaneously employing the working gas as a reactor coolant, is obtained by providing a second pressure reduction turbine to follow the reactor, thus departing from the embodiment as shown in FIG. 3. This modification affords maintaining a larger temperature difference between inlet and outlet at the reactor. FIG. 4 is a schematic temperature-pressure cycle diagram of such a direct circulatory system comprising two-stage pressure reduction, precompression and partial flow compression.

FIG. 5 shows a circuit diagram of the type represented by FIG. 4, but designed for a source heated with fossil fuel. The firing or boiler plant (source) proper is denoted by 12. The heat is transferred to the gas turbine circulation system by means of a heat exchange 121. A heat exchanger 122 in the path of the heating or flue gases of the boiler serves to preheat the combustion air supplied to the firing system 12. The same purpose is served by an air preheater 123 which is connected in series with the heat exchanger 122 with respect to the flow of the heating or flue gases. The exchanger 123 is traversed by a portion of the working gas. The circuitry of the system is otherwise as in the embodiments described above. A partial current of about 15 percent having a pressure of 92 ata. and a temperature of C. is branched off the recuperative heat exchanger 19 at point b of the low-pressure side. This partial current is ducted through the air preheater 123 and is recycled at 50 C. back into the cooler 21 at point b. In this circuit diagram the startup-regulating valves and other above-described components are omitted for simplicity.

The embodiments described constitute relatively simple circuit systems. Intermediate superheating upon partial pressure reduction of the working medium is dispensed with. Such intermediate superheating is highly disagreeable with a sodiumcooled reactor, since the heat transfer onto the CO side within the intermediate superheater portion of the plant would be very poor. consequently, it would be necessary to employ soidum-CO side within the intermediate superheater portion of the plant would be very poor. Consequently, it would be necessary to employ sodium-CO heat exchangers of extremely large volume. Another disadvantage would be the complicated ducting required for passing the CO pipes twice into the reactor building and twice out of the building.

At the proposed high-pressures and limited expansion conditions of the working gas, it preserves the high density when entering into the compressors. These may consist of radial compressors which do not react as fast as axial compressors upon changes of their throughput. The known processes involving condensation and great expansion require the use of axial compressors at least in the lower pressure stages. In the event of a change in power, requiring the throughput by weight through the high-pressure stages to be changed also, the axial compressors may attain a gas flow below the pumping limit of this compressor type. To be sure, radial compressors have a slightly lower efficiency than axial compressors, but this difference is of little significance because of the relatively low compressing power and, besides, can be moderated to a great extent by using spiral-type housings with several straight-duct diffusors. It is preferable to provide the main compressor being called upon to deliver about 70 percent of the working medium, with an adjustable input guiding device in order to better adapt the performance in the partial load range to the varying CO data.

It is a particularity of the CO physical properties, that the heating-up temperature difference in the CO heater decreases at partial load operation. If this is undesirable, for example in view of reasons concerning the operation of the nuclear reactor, then a system according to the invention as exemplified by the above-described embodiments offers the possibility of stopping the separately driven auxiliary compressor, thus increasing the heating-up difference. Arranging the auxiliary compressor on a separate shaft driven by its own turbine has the further advantage that, if needed, the auxiliary turbine can continue running, thus affording some subsequent cooling of the system inclusive of the nuclear reactor previously shut down.

Of course, the auxiliary compressor 17 may also be driven through the main shaft from the main turbine. Furthermore, as introductorily mentioned, the partial current may be passed through its own winding or coil of tubes in the recuperative heat exchanger 19, thus avoiding the necessity of providing a tap at the tube winding stack 20. In a system of the latter kind, the flow delivered by the auxiliary compressor may be passed separately through the CO heater, thus providing a completely independent auxiliary compressor turbine system which may also run on a lower high-pressure level than the main flow of working medium. The branched-off auxiliary flow in such a case is preferably provided with a type ofoverflow with the aid of a check valve which connects this flow with the main flow on the high-pressure side. Such a separate auxiliary flow system can be started up without the use of a bypass.

The induction temperature of the auxiliary compressor need not correspond exactly to the CO temperature at the transition from the recuperator to the cooler. This induction temperature may also be reduced, for example, by applying the mixing circuit extending through the valves and 36 as will be apparent from FIG. 2. In the latter case the necessary speed of the auxiliary compressor decreases and the total efficiency is slightly reduced.

It will be understood that when using nuclear reactors as a source of heat, these may operate with coolants other than sodium. This applies, for example, to reactors cooled with helium or CO Gas cooling is applicable, for example, with fast breeder reactors, graphite-moderated reactors or heavywater moderated reactors. For safety reasons such systems often require an indirect circulation involving the use of a primary-secondary heat exhanger. If, with a Co -cooled reactor, the primary as well as the secondary circuits are operated with the same medium, namely CO gas, considerable leakage between primary and secondary circulation is permissible, such as in the order of l ton CO per day, without the danger of contaminating the turbine circulation system since the latter is under a higher pressure than the primary circulation. The indirect type of system has the disadvantage ofconsuming additional power for the blower needed to circulate the medium in the primary circuit. In many cases, however, the liberty of selecting the secondary pressures for optimum performance, compensates for this disadvantage to a large extend in spite of the lower turbine inlet temperature, for example 464 C., occurring in a Co -cooled fast breeder reactor. Illustrative in this respect is the diagram in FIG. 2b. In this example, the recuperator outlet temperature (point 9 in the diagram) is so low that its distance from the end temperature (point 7) of the auxiliary flow compression is only moderate or small. This applies particularly because the pressure ratio in the turbine according to FIG. 2a has been somewhat increased, which causes the temperature at point 9 to be lower and at point 7 to be higher. In this case no tap at the recuperative heat exchanger is needed which is advantageous for technological and financial reasons. It suffices to simply mix the partial flows and to pass the working medium at the mixing temperature (point 8) into the heater, i.e., the primary-secondary heat exchanger. Another remarkable application of the indirect CO, turbine process results in conjunction with a hellum-cooled high-temperature reactor. For example, an outlet temperature of 750 C. at the reacotr permits using a primarysecondary heat exchanger of a relatively very small heating surface, ifa temperature of 590 C. at the CO turbine is sufficient. At such a temperature, the CO turbine process, in analogy to FIG. 2, furnishes a net efficiency of more than percent of the power station. In general, it should also be understood that CO turbines in conjunction with gas-cooled nuclear reactors can also be employed for driving the pump or blower which circulates the coolant in the primary circuit. With respect to the mechanical design of the recuperative heat exchanger 19 as well as of the coolers, reference may be had to my above-mentioned application Ser. NO. 772,640, according to which these apparatus may have a prestressed concrete containerin common.

To those skilled in the art, it WIII be obvious upon a study of this disclosure that my invention permits of various modifications and can be given embodiments other than illustrated and described herein, without departing from the essential features of the invention and within the scope of the claims annexed hereto.

I claim:

1. A gas turbine powerplant for operation with heat from nuclear or fossil fuel, comprising a circulatory system contain ing gaseous working medium and having heat source means for heating said medium and at least one turbine connected to said source means, a recuperative heat exchanger interposed in said system serially with said turbine and said source means, a plurality of compressors, two of said compressors forming paths for respective partial flows of the total flow of medium and being connected to respectively different temperature stages of said recuperative heat exchanger at the high-pressure side thereof, cooling means connected in said system behind said turbine and ahead of said source means, the median specific heat of said medium at the high-pressure side of said recuperative heat exchanger being more than 5 percent than at the lower-pressure side, and the suction pressure of at least one of said two compressors at full load being above the critical pressure magnitude.

2. In a powerplant according to claim 1, said system having at the inlet of each of said two compressors a gaseous medium density of at least 100 kg./m.

3. In a powerplant according to claim 1, each of said two compressors having its own drive turbine connected to said source means for operation by said gaseous medium heated by said source means.

4. In a powerplant according to claim 1, said two compressors having substantially the same suction pressure above said critical magnitude.

5. In a powerplant according to claim 1, one of said two compressors having in said system a gas induction point ahead of one of said cooling means, and said other compressor having its induction point arrear of said other cooling means.

6. A powerplant according to claim 1, wherein said gaseous working medium is carbon dioxide.

7. In a powerplant according to claim 1, said heat source means comprising a heat exchanger secondarily connected in said system, and a nuclear reactor with which said latter exchanger is primarily connected to receive heat generated in said reactor.

8. In a powerplant according to claim 1, said heat source means comprising a nuclear reactor, said gaseous working medium constituting a coolant for directly cooling said reactor.

9. A powerplant according to claim 8, comprising at least two turbines for useful mechanical power generation, said two turbines being connected in said system ahead and arrear respectively of said reactor.

10. In a powerplant according to claim 1, said heat source means comprising a fossil fuel boiler plant having combustion air preheater means connected to said system for preheating the air at least partially by residual heat of said circulatory system for the gaseous working medium.

11. In a powerplant according to claim 1, one of said two compressors being the main compressor and the other an auxiliary compressor of the system, said main compressor having a larger throughput of gaseous medium than said auxiliary compressor, and regulating means for partial load operation of the plant, said regulating means being in connection with said auxiliary compressor. 

1. A gas turbine powerplant for operation with heat from nuclear or fossil fuel, comprising a circulatory system containing gaseous working medium and having heat source means for heating said medium and at least one turbine connected to said source means, a recuperative heat exchanger interposed in said system serially with said turbine and said source means, a plurality of compressors, two of said compressors forming paths for respective partial flows of the total flow of medium and being connected to respectively different temperature stages oF said recuperative heat exchanger at the high-pressure side thereof, cooling means connected in said system behind said turbine and ahead of said source means, the median specific heat of said medium at the high-pressure side of said recuperative heat exchanger being more than 5 percent than at the lower-pressure side, and the suction pressure of at least one of said two compressors at full load being above the critical pressure magnitude.
 2. In a powerplant according to claim 1, said system having at the inlet of each of said two compressors a gaseous medium density of at least 100 kg./m.2.
 3. In a powerplant according to claim 1, each of said two compressors having its own drive turbine connected to said source means for operation by said gaseous medium heated by said source means.
 4. In a powerplant according to claim 1, said two compressors having substantially the same suction pressure above said critical magnitude.
 5. In a powerplant according to claim 1, one of said two compressors having in said system a gas induction point ahead of one of said cooling means, and said other compressor having its induction point arrear of said other cooling means.
 6. A powerplant according to claim 1, wherein said gaseous working medium is carbon dioxide.
 7. In a powerplant according to claim 1, said heat source means comprising a heat exchanger secondarily connected in said system, and a nuclear reactor with which said latter exchanger is primarily connected to receive heat generated in said reactor.
 8. In a powerplant according to claim 1, said heat source means comprising a nuclear reactor, said gaseous working medium constituting a coolant for directly cooling said reactor.
 9. A powerplant according to claim 8, comprising at least two turbines for useful mechanical power generation, said two turbines being connected in said system ahead and arrear respectively of said reactor.
 10. In a powerplant according to claim 1, said heat source means comprising a fossil fuel boiler plant having combustion air preheater means connected to said system for preheating the air at least partially by residual heat of said circulatory system for the gaseous working medium.
 11. In a powerplant according to claim 1, one of said two compressors being the main compressor and the other an auxiliary compressor of the system, said main compressor having a larger throughput of gaseous medium than said auxiliary compressor, and regulating means for partial load operation of the plant, said regulating means being in connection with said auxiliary compressor.
 12. In a powerplant according to claim 11, said regulating means being also connected to said main compressor for response to induction temperature.
 12. In a powerplant according to claim 11, said regulating means being also connected to said main compressor for response to its induction temperature. 